1. Field of the Invention
The present invention relates in general to a digital conversion system for a color video signal wherein the analog color video signal is converted to a digital color video signal. This invention is particularly applicable where a composite color video signal and primary color video signals are selectively applied.
2. Description of the Prior Art
In a magnetic recording apparatus for example, which records a composite color video signal of the NTSC system and also can record component color video signals consisting of the three primary color signals, red, green and blue, apparatus such as shown in FIG. 1 is utilized in prior art systems wherein at least four analog to digital circuits are required.
In FIG. 1, for example, an analog composite color video signal is supplied to an input terminal 1 of an analog to digital converter 3 which has an output terminal 4. The analog component color video signals R (red), G (green) and B (blue) are respectively supplied to input terminals 2R, 2G, and 2B of analog to digital converters 5R, 5G and 5B, respectively. For the case when the input signal is a composite color video signal, the input terminal 1 is selected and an analog composite color video signal is supplied from the input terminal 1 to the A/D converter 3. The A/D converter 3 converts a wide band composite color video signal having a band width of about 6 MHz. An A/D converter which is capable of processing at high speeds is utilized for the analog to digital converter 3, and is supplied to the output terminal 4.
For the case where an input signal comprises component color video signals consisting of three primary color signals, the input terminals 2R, 2G and 2B are selected and the three primary color analog signals R, G and B are respectively supplied from the input terminals 2R, 2G and 2B to the analog to digital converters 5R, 5G and 5B. These A/D converters 5R, 5G and 5B respectively convert the wide band component color video signals R, G and B from analog to digital signals. Analog to digital converters which can process signals at high speeds are used for this purpose. The component color video signals R, G and B which have been digitized by the A/D converters 5R, 5G and 5B are supplied to a matrix circuit 6, which produces a luminance signal Y and color difference signals B-Y and R-Y which are supplied to the output terminals 7, 8 and 9, respectively.
Thus, conventional digital conversion systems such as illustrated in FIG. 1 require a total of four A/D converters 3, 5R, 5G and 5B to digitize a composite color video signal and three primary color component video signals R, G and B. Furthermore, such A/D converters must perform processing at high speed. The large number of A/D converters make the system very expensive which is a distinct disadvantage.